Virtual reality system locomotion interface utilizing a pressure-sensing mat

ABSTRACT

A virtual reality system transposes a user&#39;s position and movement in real space to virtual space. The virtual reality system includes a locomotion interface that outputs signals indicative of a user&#39;s position in real space. The locomotion interface includes a pressure-sensing mat having a base layer, a plurality of pressure sensing elements formed over the base layer, and a top layer formed over the plurality of pressure-sensing elements, and a base around which the pressure sensing mat is disposed, the pressure-sensing mat being freely moveable about the base. The plurality of pressure sensing elements output a signal indicative of pressure applied to the top layer. A virtual reality processor uses the signals output by the locomotion interface to produce an output indicative of the user&#39;s position in the virtual space corresponding to the user&#39;s position and movement in the real space. A display uses the output from the virtual reality processor to produce an image of the virtual space.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] This invention relates to virtual reality systems that can beused to fully immerse a user in virtual space.

[0003] 2. Description of Related Art

[0004] Virtual reality is a computer-generated environment in which auser is immersed. Actions of the user are translated by a computer intoinputs that effect the virtual environment (VE). Virtual reality systemsmay stimulate naturally occurring senses, such as sight, sound, touchand movement, so that a user can navigate through a virtual environmentas if in the real world.

[0005] A major challenge to virtual reality system designers is todesign a virtual reality system that allows natural human locomotion.Previous virtual reality systems that allow the user to move naturallyrequire complex and expensive equipment. Other virtual reality systemsabandon the concept of natural human locomotion, using simple hardwarethat allow the user to navigate through the virtual environment withartificial gestures, such as flying in the virtual space in thedirection the user's finger is pointing.

[0006] Known virtual reality systems include treadmill devices thattrack the user's movement on the treadmill. Such a device is disclosedin U.S. Pat. No. 5,562,572 to Carmein. Although these treadmill devicesallow movement in the user's upright position, they do not allowmovement in the user's prone position. They also cannot sense whetherthe user is in the standing, crawling or prone position. Further, thesetreadmill devices are often mechanically complicated, and are thusencumbered by the inherent lag times and momentum problems associatedwith moving mechanical masses.

[0007] Other known virtual reality systems allow the user to move in theprone position, but sacrifice natural motion. For example, one knowndevice includes a simple foot-pedal interface, similar to theaccelerator of an automobile. The foot-pedal allows the user to moveforward or backward, depending on where the user presses the foot-pedal.In this system, the user always moves toward the center of the field ofview, and the field of view is rotated if the user turns his head past acertain angle. Although this system allows a user to navigate from anyposture, the user must be in constant contact with the foot-pedal tonavigate. It also does not enable the user to move naturally.

SUMMARY OF THE INVENTION

[0008] In various exemplary embodiments, the virtual reality systemaccording to one aspect of this invention includes a pressure-sensingmat that outputs signals indicative of a user's position in real space.A virtual reality processor uses the signals output by thepressure-sensing mat to produce an output indicative of the virtualspace corresponding to the user's position and movement in real space. Adisplay device uses the output from the virtual reality processor toallow the user to be fully immersed in the virtual space.

[0009] In various exemplary embodiments, the pressure sensing matincludes a base layer, a plurality of pressure sensing elements formedover the base layer, and a top layer formed over the plurality ofpressure-sensing elements. The plurality of pressure sensing elementsoutput a signal indicative of pressure applied to the top layer.

[0010] This invention provides a virtual reality system that has asimple design and that allows a user to move naturally in any directionfrom any posture (e.g., standing, crawling, prone). The virtual realitysystem according to this invention has many advantages over previousvirtual reality systems. The enhanced flexibility of the variousexemplary embodiments of the system according to this invention allows auser to move forward, backward, or sideways from a prone, crawling orstanding position. Thus, the virtual reality system according to thisinvention has many applications, such as, for example, enhanced militarytraining, realistic video game environments, and a broad range ofmedical and therapeutic applications.

[0011] These and other features and advantages of this invention aredescribed in, or are apparent from, the following detailed descriptionof various exemplary embodiments of the systems and methods according tothis invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Various exemplary embodiments of this invention will be describedin detail, with reference to the following figures, wherein:

[0013]FIG. 1 illustrates one exemplary embodiment of a virtual realitysystem according to this invention;

[0014]FIG. 2 illustrates one exemplary embodiment of the pressuresensing mat according to this invention;

[0015]FIG. 3 shows one exemplary embodiment of a pressure sensitiveresistor usable with the various exemplary embodiments of the virtualreality system according to this invention;

[0016]FIG. 4 illustrates the equivalent circuit of the pressure sensingmat according to this invention;

[0017]FIG. 5 is a block diagram of an exemplary embodiment of thevirtual reality processor according to this invention; and

[0018]FIG. 6 illustrates a cross section of an exemplary embodiment of alocomotion interface according to this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019]FIG. 1 illustrates one exemplary embodiment of a virtual realitysystem according to this invention. The virtual reality system 1includes a pressure sensing mat 100, a virtual reality (VR) processor200, and a display 400. It should be appreciated that the variousexemplary embodiments of the virtual reality system according to thisinvention can have any number and configuration of components that use apressure sensing mat to sense the user's movement in order to generate avirtual environment.

[0020]FIG. 2 illustrates one exemplary embodiment of the pressuresensing mat 100 according to this invention. The pressure sensing mat100 includes a semi-rigid base layer 120. Any suitable material can beused for the base layer 120, such as, for example, plastic, hardwood,and polycarbonate (lexan). A grid 140 (i.e., a two-dimensional array) ofpressure sensing elements 150-1 to 150-n is formed over the base layer120. A top layer 160 is formed over the grid 140. Any suitable layer canbe used for the top layer 160, such as, for example, rubber, naturalrubber, buna's rubber, and fabric reinforced negro rubber, is preferred.

[0021] The pressure sensing elements 150-1 to 150-n of the grid 140detect the pressure applied to fixed points on the top layer 160 of thepressure sensing mat 100. Any suitable pressure sensing device can beused for the pressure sensing elements 150-1 to 150-n, such as, forexample, electromechanical pressure sensors. In general, any known orlater discovered pressure sensing device can be used for the pressuresensing elements 150-1 to 150-n.

[0022] In the exemplary embodiment shown in FIG. 1, the pressure sensingelements 150-1 to 150-n include force sensitive resistors. As is knownin the art, force sensitive resistors include elements that act assimple voltage dividers. FIG. 3 shows one exemplary embodiment of apressure sensitive resistor 180 usable with the various exemplaryembodiments of the virtual reality system according to this invention.The pressure sensing elements 150-1 to 150-n include correspondingpressure sensitive resistors 180-1 to 180-n. Each pressure sensitiveresistor 180 includes an upper film 181, a lower film 182, a firstelectrode pattern 183 formed over the lower film 182, a second electrodepattern 184 formed over the upper film 181 so as to oppose the electrodepattern 183, and a pressure-sensitive conductor 185 formed over thesecond electrode pattern 184. When the upper film 181 is pressed, thepressure sensitive conductor 185 is compressed between the first andsecond electrode patterns. As is known in the art, the resistance of thepressure sensitive conductor 185 is lowered when compressed.Accordingly, voltage output of the pressure sensitive resistor 180 willvary with applied pressure. For more details of a pressure-sensitiveresistor, see U.S. Pat. No. 5,948,990, the disclosure of which isincorporated herein by reference.

[0023]FIG. 4 illustrates the equivalent circuit of the pressure sensingmat 100. The voltage outputs Vout-1 to Vout-n correspond to respectivepressure sensing elements 150-1 to 150-n that make up the grid 140. Auser applies pressure to points on the pressure sensing mat 100 as theuser navigates through the virtual reality environment. The appliedpressures alter the resistance of the pressure sensitive resistors 180-1to 180-n, and thus the voltage output of each of the correspondingpressure sensing elements 150-1 to 150-n varies as the user moves. Thegrid 140 produces a voltage output that can be analyzed to generate apattern that shadows the user's movements in the virtual space.

[0024]FIG. 5 is a block diagram of an exemplary embodiment of thevirtual reality processor 200. The virtual reality processor includes acontroller 210, a memory 220 (including RAM and ROM, for example), apattern generation device 230, a motion identification device 240, avirtual environment rendering device 250, an input interface 260, and anoutput interface 270. The controller 210 interfaces with the othercomponents 220-270 using a control/data bus 280. Although the exemplaryvirtual reality processor 200 uses a bussed architecture, it should beappreciated that the exemplary virtual reality processor 200 can use anyknown or later developed architectures, including ASIC, a programmedgeneral purpose computer, discrete logic devices, etc.

[0025] Under control of the controller 210, the input interface 260 canreceive analog voltage signals from the pressure sensing elements 150-1to 150-n. The input interface 260 can include an analog to digitalconverter that converts the analog voltage signals to digital signals.The input interface 260 can input the digital signals to the memory 220for storage.

[0026] Next, the controller 210 can provide the digital signals storedin the memory 220 to the pattern generation device 230. The patterngeneration device 230 samples the digital signals stored in the memory220 at regular intervals and generates a pattern based on the digitalsignals at the regular intervals. The patterns generated by the patterngeneration device 230 represent various positions of the user on thepressure sensing mat 100.

[0027] The controller 210 transfers the patterns generated by thepattern generation device 230 to the motion identification device 240.The motion identification device 240 can include a pattern recognitiondevice (not shown) that identifies a given pattern with a correspondingposition of the user. The pattern recognition device can identify apattern by comparing the pattern with a database of patterns stored inthe memory 220. The pattern recognition device can also recognize thepattern based on the size, shape and/or pressure distribution of thepattern. For example, if the pattern is larger than a predeterminedthreshold size, the pattern recognition device will recognize thepattern as a “prone user position” pattern. Similarly, if the matoutputs signals indicative of two patterns of a similar size thatalternately move, the processor determines that the user is upright(e.g., walking, running or standing (if the two patterns do not move)).If more than two smaller moving patterns are detected, the user isdetermined to be crawling. The patterns stored in the memory 220 canprovide examples for a neural network to learn how to identify differentpatterns.

[0028] Based on the posture and directional information determined bythe processor, the virtual environment (i.e., the displaying image) isappropriately altered.

[0029] A series of user positions identified by the pattern recognitiondevice can be stored in the memory 220 during fixed intervals as theuser navigates through the virtual environment. Preferably, the centroidof each of the patterns in the series of patterns is tracked as the usermoves on the pressure sensing mat 100. The motion identification device240 can sample the series of user positions at the end of the fixedintervals and identify the motion of the user during the fixed intervalsbased on the series of user positions. The motion includes, for example,direction (forward, backward, left, right, etc.) and speed. The patternsalso can be analyzed to determine the posture (standing, crawling,prone) of the user.

[0030] The direction that the user is facing is determined by a sensorthat can be directly attached to the user. In embodiments, the sensorcan be a magnetic tracker attached to the user's waist that determinesthe direction the waist is facing. The virtual reality system accordingto this invention provides significant advantages over known virtualreality systems in that only a single sensor needs to be directlyattached to the user. Thus, the user is relatively free from cumbersomesensor wiring and devices.

[0031] The controller 210 can transpose the motion of the user into thevirtual environment generated by the virtual environment renderingdevice 250. Data for the virtual environment, including virtual objects,can be stored in the memory 220. The virtual environment renderingdevice 250 can update the virtual environment at given intervals basedon the data stored in the memory 220. The virtual environment renderingdevice 250 can update the virtual space each time the user's motion isidentified. Thus, as the user moves through the virtual space, the usercan effect, and can be effected by, the virtual environment. Forexample, as the user navigates through the virtual space, the user'sperspective in the virtual space can change, virtual objects can enterthe user's path, and the user can move virtual objects.

[0032] The controller 210 can control the output interface 270 to outputvirtual reality environment data to the display 400. Although thedisplay 400 is shown in FIG. 1 as a head-mounted display, any known orlater discovered display can be used. Preferably, the display providesthe user with the ability to see, hear, smell and/or touch in thevirtual world so that the user is fully immersed in the virtual space.

[0033] In embodiments, it is conceivable that the pressure sensing mat100 can be as large as required to allow the user to move as if the userwas in the virtual space. For example, the pressure sensing mat 100 canbe made to cover the floor of a large field or room. Alternatively, ifspace is limited, the pressure sensing mat 100 can be made smaller, inwhich case the user would be required to move in a bounded area or move“in place”. Further, the pressure sensing mat 100 can be arranged in abelt-like manner, such as in the form of a tread-mill. For example, FIG.6 illustrates a cross section of a locomotion interface 300 according toan embodiment of this invention including a pressure sensing mat 305wrapped around a spheroid base 330. As shown in FIG. 6, the pressuresensing mat 305 includes a base layer 310, a grid 315 of pressuresensing elements 320-1 to 320-n formed over the base layer 310, and atop layer 325 formed over the grid 315. The pressure sensing mat 305 canbe held on to the surface of the spheroid base 330 by its ownelasticity, thus making the contact between the spheroid base 330 andthe pressure sensing mat 305 relatively frictionless.

[0034] The locomotion interface 300 includes a housing 335 that retainsthe pressure sensing mat 305 and the spheroid base 330. Passive casters335 can be mounted in the housing 335 to allow the pressure sensing mat305 to move freely in all directions in the housing 335.

[0035] In this embodiment, the locomotion interface 300 must have thecapability of allowing a user to feel as if he/she can move in alldirections for an “infinite” distance. Thus, the pressure sensing mat305 must be able to move underneath the user as the user “moves” in thevirtual environment. However, although the pressure sensing mat 305moves will little friction on the spheroid base 330, the mass of thepressure sensing mat 305 will not allow the user to propel the pressuresensing mat 305 underneath him/herself as the user moves. Thus, in thisembodiment, the pressure sensing mat 305 is mechanically actuated tomove underneath a user. For example, as shown in FIG. 6, a steerableroller 340 is disposed in the housing 335, and the steerable roller isin frictional contact with the pressure sensing mat 305. The roller 340is steerable about a first axis 350 and a second axis 360. The firstaxis 350 is perpendicular to the second axis 360. A first motor 345powers the roller 340 about the first axis 350, and a second motor 355powers the roller 340 about the second axis 360. The thrust vectorsgenerated by the roller 340 cause the pressure sensing mat 305 to slidearound the spheroid base 330 in all directions.

[0036] A sensor (not shown) can be placed above the locomotion interface300 to sense the direction in which the user is facing. The sensed userdirection can then be used to determine the appropriate thrust vector tobe generated by the roller 340, to thereby move the pressure sensing mat305 underneath the user. For example, if the sensor determines that theuser is facing a first direction, the roller 340 can be controlled tocreate a thrust vector in the first direction to thereby move thepressure sensing mat underneath the user in a second direction oppositethe first direction.

[0037] The roller 340, casters 335 and other mechanical parts of thelocomotion interface 300 may interfere with accurate pressure sensing bythe pressure sensing mat 305. Further, the pressure sensing mat 305 willbe moving underneath the user as the user “moves” in the virtualenvironment, which will also diminish the accuracy of the pressuresensing. In order to solve these problems, when the user first steps onthe pressure sensing mat 305, an initialization procedure can be done inwhich the users position on the pressure sensing mat 305 is determined.

[0038] The virtual reality system 1 can be implemented as softwareexecuting on a programmed general purpose computer, a special purposecomputer, a microprocessor or the like.

[0039] While the invention has been described with reference toexemplary embodiments thereof, it is to be understood that the inventionis not limited to the preferred, exemplary embodiments or constructions.To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements. In addition, while thevarious elements of the exemplary embodiments are shown in variouscombinations and configurations, which are exemplary, other combinationsand configurations, including more, less or only a single element, arealso within the spirit and scope of the invention.

What is claimed is:
 1. A locomotion interface that provides inputsignals, indicative of a user's movement, to a virtual reality system,the locomotion interface comprising: a pressure-sensing mat including abase layer, a plurality of pressure sensing elements formed over thebase layer, and a top layer formed over the plurality ofpressure-sensing elements, wherein the plurality of pressure sensingelements output signals indicative of pressure applied to the top layer;and a base around which the pressure sensing mat is disposed, thepressure-sensing mat being freely moveable about the base.
 2. Thelocomotion interface of claim 1, wherein the base is in the shape of aspheroid.
 3. The locomotion interface of claim 1, further comprising ahousing that retains the pressure-sensing mat and the base.
 4. Thelocomotion interface of claim 3, further comprising a plurality ofcasters disposed between the housing and the pressure-sensing mat, thecasters allowing the pressure-sensing mat to move in the housing.
 5. Thelocomotion interface of claim 3, further comprising: a roller disposedin the housing, the roller being in frictional contact with thepressure-sensing mat; a first motor that rotates the roller about afirst axis; and a second motor that rotates the roller about a secondaxis, the second axis being perpendicular to the first axis, wherein therotation of the roller generates thrust vectors that move thepressure-sensing mat in all direction.
 6. The locomotion interface ofclaim 1, wherein the plurality of pressure-sensing elements make up agrid.
 7. The locomotion interface of claim 1, wherein the plurality ofpressure-sensing elements comprise force sensitive resistors.
 8. Thelocomotion interface of claim 1, wherein the base layer comprises asemi-rigid material.
 9. The locomotion interface of claim 1, wherein thebase layer comprises plastic.
 10. The locomotion interface of claim 1,wherein the top layer comprises rubber.
 11. A virtual reality systemcomprising the locomotion interface of claim
 1. 12. A virtual realitysystem that transposes a user's position and movement in real space tovirtual space, the virtual reality system comprising: a locomotioninterface that outputs signals indicative of a user's position in realspace, the locomotion interface including a pressure-sensing matincluding a base layer, a plurality of pressure sensing elements formedover the base layer, and a top layer formed over the plurality ofpressure-sensing elements, the plurality of pressure sensing elementsoutput signals indicative of pressure applied to the top layer, and abase around which the pressure sensing mat is disposed, thepressure-sensing mat being freely moveable about the base; a virtualreality processor that uses the signals output by the locomotioninterface to produce an output indicative of the user's position in thevirtual space corresponding to the user's position and movement in thereal space; and a display that uses the output from the virtual realityprocessor to produce an image of the virtual space.
 13. The virtualreality system of claim 12, wherein the display is a head mounteddisplay.
 14. The locomotion interface of claim 12, wherein the base isin the shape of a spheroid.
 15. The locomotion interface of claim 12,further comprising a housing that retains the pressure-sensing mat andthe base.
 16. The locomotion interface of claim 15, further comprising aplurality of casters disposed between the housing and thepressure-sensing mat, the casters allowing the pressure-sensing mat tomove in the housing.
 17. The locomotion interface of claim 15, furthercomprising: a roller disposed in the housing, the roller being infrictional contact with the pressure-sensing mat; a first motor thatrotates the roller about a first axis; and a second motor that rotatesthe roller about a second axis, the second axis being perpendicular tothe first axis, wherein the rotation of the roller generates thrustvectors that move the pressure-sensing mat in all direction.
 18. Thevirtual reality system of claim 12, wherein the plurality ofpressure-sensing elements make up a grid.
 19. The virtual reality systemof claim 12, wherein the plurality of pressure-sensing elements compriseforce sensitive resistors.
 20. The virtual reality system of claim 12,wherein the base layer comprises a semi-rigid material.
 21. The virtualreality system of claim 12, wherein the base layer comprises plastic.22. The virtual reality system of claim 12, wherein the top layercomprises rubber.
 23. The virtual reality system of claim 12, whereinthe virtual reality processor comprises: a pattern generator that usesthe signals output from the locomotion interface to generate a pluralityof corresponding patterns; a motion identifier that uses the pluralityof patterns generated by the pattern generator to identify acorresponding plurality of user positions and user movements; and avirtual environment renderer that uses the identified user positions andmovements to generate a virtual space such that the user can effect, andbe effected by, the virtual space.
 24. The virtual reality system ofclaim 23, wherein the plurality of positions identified by the motionidentifier comprise at least one of a prone user position, a crawlinguser position, and a standing user position.
 25. The virtual realitysystem of claim 23, wherein the plurality of motions identified by themotion identifier comprise at least one of a backward user motion, asideways user motion, a forward user motion, and a diagonal user motion.26. A method of providing input signals, indicative of a user'smovement, to a virtual reality system, comprising: sensing pressureapplied to a locomotion interface having a pressure-sensing matincluding a base layer, a plurality of pressure sensing elements formedover the base layer, and a top layer formed over the plurality ofpressure-sensing elements, and a base around which the pressure sensingmat is disposed, the pressure-sensing mat being freely moveable aboutthe base
 27. The method of claim 26, further comprising: processingsignals output by the locomotion interface, in response to the sensedpressure, to produce an input signal indicative of the user's positionin virtual space corresponding to the user's position and movement inreal space.
 28. The method of claim 27, wherein the step of processingthe signals output by the locomotion interface comprises: generating aplurality of patterns that correspond to the signals output by thelocomotion interface; and identifying a plurality of user positions anduser movements that correspond to the plurality of patterns.